Earth’s oceans are crisscrossed with roughly 1.2 million km of fiber optic telecommunication cables. Researchers have now succeeded in using a fiber in a submarine cable as a passive listening system, enabling them to listen to and monitor whales.Earth’s oceans are crisscrossed with roughly 1.2 million km of fiber optic telecommunication cables. Researchers have now succeeded in using a fiber in a submarine cable as a passive listening system, enabling them to listen to and monitor whales.